This invention relates to a cap for sealing containers containing liquid samples such as blood and, more specifically, pertains to a stopper having an opening biased by a spring element into a closed position which opening is adapted to receive a pipette for aspirating the samples of the liquid.
The use of stoppers which are penetrable by a sharp instrument such as a needle for removal of the contents of the container have been in use for years. An early example of a stopper capable of being penetrated is found in U.S. Pat. No. 1,616,274 issued on Feb. 1, 1927 to Mulford.
More recently, however, it has become common place to use stoppers which accommodate more blunt instruments for removal of samples of the liquid for investigation and analysis. For example, it has become extremely well known that the multitude of biological samples, particularly blood and blood serums, awaiting analysis must be in closed containers to avoid the hazards of exposing medical personnel and the potential of degrading the sample through evaporation. The primary reason for desiring easy access to the container is to allow either the manual aspiration of the liquid with a pipette or the like or automated aliquoting of the sample by the testing apparatus. Such sampling techniques are carried out with disposable plastic pipettes or delicate instrument probes, neither of which is capable of piercing a rubber septum.
While the prior art is replete with examples of penetrable stoppers or caps sealing containers storing fluid for analysis, the problem was and still is to ensure that nothing contaminates the fluid sealed in the container before analysis and that the fluid itself does not escape or otherwise leak from the container either before or after sampling. Typical prior art caps involve the use of a body that fits within the cavity of a sample container and is provided with a closable opening or slit for entry of blunt, but narrow, hollow cylindrical object such as a pipette for removing a portion of the liquid contained therein. The body is made from a resilient material which is stretched by the insertion of the pipette into the slit. The slit closes due to the natural bias of the material after the pipette is removed, thus in effect forming a one-way type of valve arrangement.
An example of such a cap for this purpose is shown in U.S. Pat. No. 4,515,752 issued May 7, 1985 to Miramanda. The cavity of the cap is closed by resilient body having a plurality of pie-shaped segments which when pressed together form a plurality of closed slits. The slits are maintained closed by the compression of the cap within the container. When a pipette is pushed against the segments, they part and then come together again after the pipette is withdrawn due to the resiliency of the material forming the segments.
The major drawbacks with prior art type of caps involving one way type of valves are complexity and cost. Once used, the caps, of necessity, are thrown away or at least recycled. Thus, simplicity of construction to maintain low costs is of paramount consideration. Additionally, the caps must be of sound construction and perform well despite the low cost. Specifically, it is desirable that the cap be easily accessible to blunt ended instruments such as pipette for aspiration of the sample housed within the container and provided with a positive feature for maintaining the opening in the cap closed other than through the natural resiliency of the material used in its construction. It is further desirable that the opening be biased closed with such a positive feature along a substantial portion of its length to prevent inadvertent opening to occur even when urged closed at its midpoint.